Is Vitamin D Overhyped?

Are Clouds Gathering For the Sunshine Vitamin?

Author: Dr. Stephen Chaney

We’ve known for years that vitamin D plays an essential role in calcium metabolism and is important for bone health. In fact, the use of vitamin D to prevent and cure rickets is one of the greatest success stories in the field of nutrition.

However, in recent years a number of studies have suggested that adequate vitamin D status was also important in reducing the risk of cancer, heart disease, diabetes, infectious diseases and autoimmune diseases – as well as overall mortality. Suddenly it seemed as if vitamin D could leap over tall buildings in a single bound (I realize that I’m probably dating myself with that analogy).

So when I saw the headlines about a new study (Theodoratou et al, BMJ, 2014;348:g2035 doi: 10.1136/bmj.g2035) that concluded all of those benefits of vitamin D were unconfirmed, I was not surprised. After all there have been many examples of periods in which individual vitamins were reported to have miraculous benefits – only to have most of those benefits debunked by subsequent studies. I fully expected that would be the theme of this issue of “Health Tips From the Professor”.

But when I read the article I found that the study had multiple flaws (more about that latter). I also discovered that the same issue of the British Medical Journal had another, much better designed, study that came to the exact opposite conclusion (Chowdhury et al, BMJ 2014;348:g1903 doi: 10.1136/bmj.g1903).

Funny how only the first study made it into the headlines. It’s only the negative news that sells.

Is Vitamin D Overhyped?

The first study was a very large meta-analysis that included 107 systematic reviews, 74 meta-analyses of observation studies (studies that compare population groups) and 87 meta-analyses of randomized, placebo controlled trials. In case you were wondering, the total number of patients enrolled in these studies must have numbered in the hundreds of thousands.

The authors of the study reported that:

There was no relationship between vitamin D intake and cancer, heart disease, autoimmune disease, infectious diseases, diabetes and other diseases. In other words, they concluded that most of the recent excitement about vitamin D was just hype.

There was also no evidence that vitamin D increased bone density or reduced the risk of fractures and falls in older people – in contrast to many previous studies.

Based on this evidence the authors said “universal conclusions about vitamin Ds benefits cannot be drawn [from current data]” and that vitamin D “might not be as essential as previously thought in maintaining bone mineral density”.

Both of those statements are pretty revolutionary, but a study this large has to be true – right? The answer is a definite maybe. The problem is that many of the studies included in this meta-analysis were poorly designed by today’s standards. Remember the old saying “garbage in, garbage out”.

The Study Is Flawed

My specific criticisms of the study are:

1) The conclusions about vitamin D and bone density were seriously flawed. The authors acknowledged that previous studies have shown that calcium and vitamin D together increased bone density, but they considered calcium to be a confounding variable and only included clinical trials using vitamin D supplementation alone. That shows a complete misunderstanding of the biochemical role of vitamin D.

The purpose of vitamin D is to maintain constant levels of blood calcium, not to build strong bones.

When blood levels of calcium are high, vitamin D lowers it by depositing the calcium in bones.

When blood levels of calcium are low, vitamin D raises it by leaching calcium from bone.

That’s why vitamin D and calcium work together. It is utter nonsense to expect vitamin D to increase bone density or prevent fractures unless you make sure that calcium intake is at least adequate.

2) Most studies of vitamin D supplementation did not stratify the data based on low versus high levels of 25-hydroxy vitamin D at the beginning of the study. That’s important because you would only expect vitamin D supplementation to be of benefit in people with low levels of 25-hydroxy vitamin D to begin with. If their 25-hydroxy vitamin D levels are already optimal, vitamin D supplementation is unlikely to be of additional benefit.

3) Finally, the authors did not separate the studies based on whether vitamin D2 or vitamin D3 was used. That’s important because some recent studies have suggested that D3 is more beneficial than D2.

Is Vitamin D Beneficial After All?

The second study came to the exact opposite conclusions. It was also a very large study. It included 73 observational studies (849,412 participants) and 22 randomized, placebo controlled studies (30,716) participants. Here is what the authors of this study concluded.

High blood levels of 25-hydroxy vitamin D decreased the risk of heart disease by 35%, cancer by 14% and overall mortality by 35%.

65% of the US population can be classified as vitamin D insufficient (blood levels of 25-hydroxy vitamin D of below 30 ng/ml) and 4% as severely deficient in vitamin D (blood levels below 10 ng/ml)

Vitamin D deficiency contributes to 13% of the deaths in the United States. For comparison the corresponding numbers for other major risk factors are: smoking – 20%, physical inactivity – 11% and alcohol – 9%.

About the only point on which the two studies agreed was that there is a need for more, better designed studies to clarify the benefits of vitamin D.

The Bottom Line:

1) Two studies were published in the April 2014 issue of the British Medical Journal. The first concluded that all of the supposed benefits of vitamin D – including increasing bone density – were not supported by the available data. The second study concluded that adequate intake of vitamin D significantly reduced deaths due to heart disease and cancer and also significantly reduced overall mortality. Somehow, only the first study made it into the headlines. Why does that not surprise me?

2) The suggestion in the first study that vitamin D may not be essential for strong bones is based on a complete misunderstanding of the role of vitamin D in the body. There are ample clinical studies showing that vitamin D and calcium together are essential for strong bones. Nobody who understands biochemistry would expect vitamin D to increase bone density in the absence of calcium, but the authors only considered studies that excluded calcium in drawing their conclusion that vitamin D did not increase bone density.

3) The only point of agreement between the two studies is that more and better studies are needed to sort out the benefits of vitamin D and what levels of vitamin D are optimal. I wholeheartedly agree.

4) My advice is to ignore the headlines telling you that vitamin D is dead. On the other hand, don’t get caught up in the hype and buy megadoses of vitamin D supplements. While the evidence is rock solid that vitamin D and calcium together are essential for strong bones, the jury is still out on some of the other health benefits of vitamin D.

5) If you are supplementing with vitamin D you should know that the RDAs for vitamin D are 600 IU for ages 1-70 and 800 IU over 70. The safe upper limit has been set at 4,000 IU. You should only go above that on a doctor’s advice.

6) However, people metabolize vitamin D with different efficiencies, so I strongly recommend that you get your blood levels of 25-hydroxy vitamin D tested and let your doctor help you determine how much vitamin D you should be getting.

7) Finally, a number of recent studies suggest that vitamin D3 may be more effective than vitamin D2, so I only recommend supplements that contain D3.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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Latest Article

A Low Carb Diet and Weight Loss

Posted January 15, 2019 by Dr. Steve Chaney

Do Low-Carb Diets Help Maintain Weight Loss?

Author: Dr. Stephen Chaney

Traditional diets have been based on counting calories, but are all calories equal? Low-carb enthusiasts have long claimed that diets high in sugar and refined carbs cause obesity. Their hypothesis is based on the fact that high blood sugar levels cause a spike in insulin levels, and insulin promotes fat storage.

The problem is that there has been scant evidence to support that hypothesis. In fact, a recent meta-analysis of 32 published clinical studies (KD Hall and J Guo, Gastroenterology, 152: 1718-1727, 2017 ) concluded that low-fat diets resulted in a higher metabolic rate and greater fat loss than isocaloric low-carbohydrate diets.

However, low-carb enthusiasts persisted. They argued that the studies included in the meta-analysis were too short to adequately measure the metabolic effects of a low-carb diet. Recently, a study has been published in the British Medical Journal (CB Ebbeling et al, BMJ 2018, 363:k4583 ) that appears to vindicate their position.

Are low carb diets best for long term weight loss?

Low-carb enthusiasts claim the study conclusively shows that low-carb diets are best for losing weight and for keeping it off once you have lost it. They are saying that it is time to shift away from counting calories and from promoting low-fat diets and focus on low-carb diets instead if we wish to solve the obesity epidemic. In this article I will focus on three issues:

How good was the study?

What were its limitations?

Are the claims justified?

How Was The Study Designed?

The investigators started with 234 overweight adults (30% male, 78% white, average age 40, BMI 32) recruited from the campus of Framingham State University in Massachusetts. All participants were put on a diet that restricted calories to 60% of estimated needs for 10 weeks. The diet consisted of 45% of calories from carbohydrate, 30% from fat, and 25% from protein. [So much for the claim that the study showed low-carb diets were more effective for weight loss. The diet used for the weight loss portion of the diet was not low-carb.]

During the initial phase of the study 161 of the participants achieved 10% weight loss. These participants were randomly divided into 3 groups for the weight maintenance phase of the study.

The diet composition of the high-carb group was 60% carbohydrate, 20% fat, and 20% protein.

The diet composition of the moderate-carb group was 40% carbohydrate, 40% fat, and 20% protein.

The diet composition of the low-carb group was 20% carbohydrate, 60% fat, and 20% protein.

Other important characteristics of the study were:

The weight maintenance portion of the study lasted 5 months – much longer than any previous study.

All meals were designed by dietitians and prepared by a commercial food service. The meals were either served in a cafeteria or packaged to be taken home by the participants.

The caloric content of the meals was individually adjusted on a weekly basis so that weight was kept within a ± 4-pound range during the 5-month maintenance phase.

Sugar, saturated fat, and sodium were limited and kept relatively constant among the 3 diets.

120 participants made it through the 5-month maintenance phase.

Do Low-Carb Diets Help Maintain Weight Loss?

The results were striking:

The low-carb group burned an additional 278 calories/day compared to the high-carb group and 131 calories/day more than the moderate-carbohydrate group.

These differences were even higher for those individuals with higher insulin secretion at the beginning of the maintenance phase of the study.

These differences lead the authors to hypothesize that low-carb diets might be more effective for weight maintenance than other diets.

What Are The Pros And Cons Of This Study?

This was a very well-done study. In fact, it is the most ambitious and well-controlled study of its kind. However, like any other clinical study, it has its limitations. It also needs to be repeated.

The pros of the study are obvious. It was a long study and the dietary intake of the participants was tightly controlled.

As for cons, here are the three limitations of the study listed by the authors:

#1: Potential Measurement Error: This section of the paper was a highly technical consideration of the method used to measure energy expenditure. Suffice it to say that the method they used to measure calories burned per day may overestimate calories burned in the low-carb group. That, of course, would invalidate the major findings of the study. It is unlikely, but it is why the study needs to be repeated using a different measure of energy expenditure.

#2: Compliance: Although the participants were provided with all their meals, there was no way of being sure they ate them. There was also no way of knowing whether they may have eaten other foods in addition to the food they were provided. Again, this is unlikely, but cannot be eliminated from consideration.

#3: Generalizability: This is simply an acknowledgement that the greatest strength of this study is also its greatest weakness. The authors acknowledged that their study was conducted in such a tightly controlled manner it is difficult to translate their findings to the real world. For example:

Sugar and saturated fat were restricted and were at very similar levels in all 3 diets. In the real world, people consuming a high-carb diet are likely to consume more sugar than people in the other diet groups. Similarly, people consuming the low-carb diet are likely to consume more saturated fat than people in the other diet groups.

Weight was kept constant in the weight maintenance phase by constantly adjusting caloric intake. Unfortunately, this seldom happens in the real world. Most people gain weight once they go off their diet – and this is just as true with low-carb diets as with other diets.

The participants had access to dietitian-designed prepared meals 3 times a day for 5 months. This almost never happens in the real world. The authors said “…these results [their data] must be reconciled with the long-term weight loss trials relying on nutrition education and behavioral counseling that find only a small advantage for low carbohydrate compared with low fat diets according to several recent meta-analyses.” [I would add that in the real world, people do not even have access to nutritional education and behavioral modification.]

What Does This Study Mean For You?

This study shows that under very tightly controlled conditions (dietitian-prepared meals, sugar and saturated fat limited to healthy levels, calories continually adjusted so that weight remains constant) a low-carb diet burns more calories per day than a moderate-carb or high-carb diet. These findings show that it is theoretically possible to increase your metabolic weight and successfully maintain a healthy weight on a low-carb diet. These are the headlines you probably saw. However, a careful reading of the study provides a much more nuanced viewpoint. For example, the fact that the study conditions were so tightly controlled makes it difficult to translate these findings to the real world.

In fact, the authors of the study acknowledged that multiple clinical studies show this almost never happens in the real world. These studies show that most people regain the weight they have lost on low-carb diets. More importantly, the rate of weight regain is virtually identical on low-carb and low-fat diets. Consequently, the authors of the current study concluded “…translation [of their results to the real world] requires exploration in future mechanistic oriented research.” Simply put, the authors are saying that more research is needed to provide a mechanistic explanation for this discrepancy before one can make recommendations that are relevant to weight loss and weight maintenance in the real world.

The authors also discussed the results of their study in light of a recent, well-designed 12-month study (CD Gardener et al, JAMA, 319: 667-669, 2018 ) that showed no difference in weight change between a healthy low-fat versus a healthy low-carbohydrate diet. That study also reported that the results were unaffected by insulin secretion at baseline. The authors of the current study noted that “…[in the previous study] participants were instructed to minimize or eliminate refined grains and added sugars and maximize intake of vegetables. Probably for this reason, the reported glycemic load [effect of the diet on blood sugar levels] of the low-fat diet was very low…and similar to [the low-carb diet].” In short, the authors of the current study were acknowledging that diets which focus on healthy, plant-based carbohydrates and eliminate sugar, refined grains, and processed foods may be as effective as low-carb diets for helping maintain a healthy weight.

This would also be consistent with previous studies showing that primarily plant-based, low-carb diets are more effective at maintaining a healthy weight and better health outcomes long-term than the typical American version of the low-fat diet, which is high in sugar and refined grains. In contrast, meat-based, low-carb diets are no more effective than the American version of the low-fat diet at preventing weight gain and poor health outcomes. I have covered these studies in detail in my book “Slaying The Food Myths.”

Consequently, the lead author of the most recent study has said: “The findings [of this study] do not impugn whole fruits, beans and other unprocessed carbohydrates. Rather, the study suggests that reducing foods with added sugar, flour, and other refined carbohydrates could help people maintain weight loss….” This is something we all can agree on, but strangely this is not reflected in the headlines you may have seen in the media.

The Bottom Line

A recent study compared the calories burned per day on a low-carb, moderate-carb, and high-carb diet. The study concluded that the low-carb diet burned significantly more calories per day than the other two diets and might be suitable for long-term weight control. If confirmed by subsequent studies, this would be the first real evidence that low-carb diets are superior for maintaining a healthy weight.

However, the study has some major limitations. For example, it used a methodology that may overestimate the benefits of a low-carb diet, and it was performed under tightly controlled conditions that can never be duplicated in the real world. As acknowledged by the authors, this study is also contradicted by multiple previous studies. Further studies will be required to confirm the results of this study and show how it can be applied in the real world.

In addition, the kind of carbohydrate in the diet is every bit as important as the amount of carbohydrate. The authors acknowledge that the differences seen in their study apply mainly to carbohydrates from sugar, refined grains, and processed foods. They advocate diets with low glycemic load (small effects on blood sugar and insulin levels) and acknowledge this can also be achieved by incorporating low-glycemic load, plant-based carbohydrates into your diet. This is something we all can agree on, but strangely this is not reflected in the headlines you may have seen in the media.

Finally, clinical studies report averages, but none of us are average. When you examine the data from the current study, it is evident that some participants burned more calories per hour on the high-carb diet than other participants did on the low carb diet. That reinforces the observation that some people lose weight more effectively on low-carb diets while others lose weight more effectively on low-fat diets. If you are someone who does better on a low-carb diet, the best available evidence suggests you will have better long-term health outcomes on a primarily plant-based, low-carb diet such as the low-carb version of the Mediterranean diet.

For more details read the article above.

These statements have not been evaluated by the Food and Drug Administration. This information is not intended to diagnose, treat, cure or prevent any disease.

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